The test could transform treatment of advanced prostate cancer through use of precision drugs designed to target mutations in the genes linked to cancer.

By testing cancer DNA in the bloodstream, researchers from Institute of Cancer Research in the UK found they could pick out which men with advanced prostate cancer were likely to benefit from treatment with new drugs called PARP inhibitors.

They also used the test to analyse DNA in the blood after treatment had started, so people who were not responding could be identified and switched to alternative therapy in as little as four to eight weeks.
The test could also be used to monitor a patient's blood throughout treatment, quickly picking up signs that the cancer was evolving genetically and might be becoming resistant to the drugs.

Researchers, including those from The Royal Marsden NHS Foundation Trust in the UK, said that their test is the first developed for a precision prostate cancer therapy targeted at specific genetic faults within tumours.

It could in future allow the PARP inhibitor olaparib to become a standard treatment for advanced prostate cancer, by targeting the drug at the men most likely to benefit, picking up early signs that it might not be working, and monitoring for the later development of resistance.

The test could help to extend or save lives, by targeting treatment more effectively, while also reducing the side- effects of treatment and ensuring patients don't receive drugs that are unlikely to do them any good.

The study, published in the journal Cancer Discovery, is also the first to identify which genetic mutations prostate cancers use to resist treatment with olaparib.

The test could potentially be adapted to monitor treatment with PARP inhibitors for other cancers.

"Our study identifies, for the first time, genetic changes that allow prostate cancer cells to become resistant to the precision medicine olaparib," said Johann de Bono, Professor at The Institute of Cancer Research.

"From these findings, we were able to develop a powerful, three-in-one test that could in future be used to help doctors select treatment, check whether it is working and monitor the cancer in the longer term," said de Bono.

"We think it could be used to make clinical decisions about whether a PARP inhibitor is working within as little as four to eight weeks of starting therapy," he said.

"Not only could the test have a major impact on treatment of prostate cancer, but it could also be adapted to open up the possibility of precision medicine to patients with other types of cancer as well," he said.